Semiconductor ceramic powder, semiconductor ceramic, and monolithic semiconductor ceramic capacitor

ABSTRACT

A SrTiO 3 -based grain boundary insulation type semiconductor ceramic contains a donor element in solid solution in crystal grains, an acceptor element at least in crystal grain boundaries, an integral width of (222) face of the crystal face of 0.500° or less, and an average powder grain size of crystal grains of 1.0 μm or less. A semiconductor ceramic is obtained by firing this ceramic, and a monolithic semiconductor ceramic capacitor is obtained by using the semiconductor ceramic. The SrTiO 3 -based grain boundary insulation type semiconductor ceramic powder has a large apparent relative dielectric constant ∈r APP  of 5,000 or more even when the average ceramic grain size of crystal grains is 1.0 μm or less and which has an excellent insulating property. The monolithic semiconductor ceramic capacitor is capable of having a large capacity through reduction in thickness and multilayering.

TECHNICAL FIELD

The present invention relates to a semiconductor ceramic powder, asemiconductor ceramic, and a monolithic semiconductor ceramic capacitor.In particular, the present invention relates to a SrTiO₃-based grainboundary insulation type semiconductor ceramic powder, a semiconductorceramic produced by sintering this powder, and a monolithicsemiconductor ceramic capacitor including the semiconductor ceramic.

BACKGROUND ART

In recent years, miniaturization of electronic components have beenadvanced rapidly as the electronics technology has been developed. Inthe field of the monolithic ceramic capacitor as well, demands forminiaturization and increases in capacity have intensified.Consequently, development of ceramic materials having high relativedielectric constants, reduction in thickness, and multilayering ofdielectric ceramic layers have been advanced.

For example, Patent Document 1 proposes a dielectric ceramic representedby a general formula: {Ba_(1-x-y)Ca_(x)Re_(y)O}_(m)TiO₂+αMgO+βMnO (whereRe represents a rare earth element selected from the group consisting ofY, Gd, Tb, Dy, Ho, Er, and Yb and α, β, m, x, and y satisfy0.001≦α≦0.05, 0.001≦β≦0.025, 1.000≦m≦1.035, 0.02≦x≦0.15, and0.001≦y≦0.06, respectively).

Patent Document 1 discloses a monolithic ceramic capacitor including theabove-described dielectric ceramic. The monolithic ceramic capacitor canhave a thickness of 2 μm per ceramic layer, the total number ofeffective dielectric ceramic layers of 5, and a relative dielectricconstant ∈r of 1,200 to 3,000 can be obtained.

The monolithic ceramic capacitor of Patent Document 1 takes advantage ofa dielectric action of the ceramic in itself. On the other hand,research and development on semiconductor ceramic capacitors based on aprinciple different from this have also been conducted intensively.

For example, Patent Document 2 proposes a SrTiO₃-based grain boundaryinsulation type semiconductor ceramic element assembly having an averagegrain size of crystal grains of 10 μm or less and a maximum grain sizeof 20 μm or less.

This grain boundary insulation type semiconductor ceramic is produced byfiring (primary firing) a ceramic compact in a reducing atmosphere toconvert it to a semiconductor and, thereafter, conducting firing(secondary firing (reoxidation)) in an oxidizing atmosphere to convertthe crystal grain boundaries to insulators, so that a capacitance isacquired at the crystal grain boundaries.

Consequently, in Patent Document 2, a semiconductor ceramic elementassembly is obtained, which is a semiconductor ceramic capacitor havinga single-layered structure and which has an apparent relative dielectricconstant ∈r_(APP) of 9,000 in the case where the average grain size ofcrystal grains is 8 μm.

In addition, Patent Document 3 proposes a method for manufacturing agrain boundary insulation type monolithic semiconductor ceramiccapacitor including a firing step to fire a laminate composed of layersformed from a semiconductor ceramic material, in which a compositioncontaining (Sr_(1-x-y)Ca_(x-y)Y_(y))_(m)(Ti_(1-z)Nb_(z))O₃ as a primarycomponent contains at least one type of secondary component selectedfrom a V oxide, a Mo oxide, and a W oxide within the range of 0.1 to 0.5percent by mole based on the molar ratio of the total amount of oxidesto the primary component after firing basis, and nickel internalelectrode layers, a reoxidation product addition step to add areoxidation product to the laminate, and a step to reoxidize thelaminate after the addition, wherein the above-described reoxidationstep is conducted through a heat treatment in a nitrogen atmosphereunder a predetermined reoxidation condition.

In Patent Document 3, a SrTiO₃-based grain boundary insulation typemonolithic semiconductor ceramic having a thickness of 3 μm persemiconductor ceramic layer and an outside dimension of 3.2 mm inlength, 1.6 mm in width, and 1.2 mm in height is prototyped, andcharacteristics of a voltage value, at which 1 mA of current passes,that is, a varistor voltage V_(1mA), of 2.49 V to 3.06 V and an apparentrelative dielectric constant ∈r_(APP) of 2,500 to 4,100 are obtained.

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 11-302072

Patent Document 2: Japanese Patent No. 2689439

Patent Document 3: Japanese Unexamined Patent Application PublicationNo. 2005-86020

DISCLOSURE OF INVENTION

In the case where reduction in thickness and multilayering of ceramiclayers are pushed forward by using the dielectric ceramic described inPatent Document 1, there are problems in that the relative dielectricconstant decreases when a bias is applied, the temperaturecharacteristic of the capacitance deteriorates, and short-circuitfailures increase sharply.

Consequently, when it is attempted to obtain a thin layer monolithicceramic capacitor having a large capacity of, for example, 100 μF ormore, the thickness of the dielectric ceramic layer is required to beabout 1 μm per layer, and the number of laminated layers is required tobe about 700 layers to 1,000 layers. However, under presentcircumstances, such a large-capacity monolithic ceramic capacitor hasnot been supplied as a general purpose product to the market.

On the other hand, the SrTiO₃-based grain boundary insulation typesemiconductor ceramics described in Patent Documents 2 and 3 exhibit asmall electric field dependence of the apparent relative dielectricconstant ∈r_(APP) and have a varistor characteristic. Therefore,breakage of the element can be avoided even when a high voltage isapplied, so that application to the field of capacitors is expected.

However, the average grain size in Patent Document 2 is a large 4 μmeven at a minimum (refer to Patent Document 2, Table 1) and, therefore,there is a limit to reduction in thickness and there is not even aremotest possibility that a large-capacity monolithic capacitor isobtained by reduction in thickness and multilayering.

With respect to Patent Document 3, since the varistor voltage V_(1mA) isa low 2.49 V to 3.06 V, as described above, it is almost practicallyimpossible to design a rated voltage for a capacitor element. Moreover,the apparent relative dielectric constant ∈r_(APP) is also a low 2,500to 4,100 and, therefore, superiority is not recognized as compared witheven a monolithic ceramic capacitor under the present situation.

The present invention has been made in consideration of theabove-described circumstances. Accordingly, it is one of the objects ofthe present invention to provide a SrTiO₃-based grain boundaryinsulation type semiconductor ceramic powder having a large apparentrelative dielectric constant ∈r_(APP) of 5,000 or more even when theaverage ceramic grain size of crystal grains is 1.0 μm or less and anexcellent insulating property, a semiconductor ceramic produced bysintering the semiconductor ceramic powder, and a monolithicsemiconductor ceramic capacitor capable of having a large capacitythrough reduction in thickness and multilayering by using thesemiconductor ceramic.

MEANS FOR SOLVING THE PROBLEMS

A donor element is contained in solid solution in the crystal grains ofthe SrTiO₃-based grain boundary insulation type semiconductor ceramic inorder to convert the ceramic to a semiconductor. In this type ofsemiconductor ceramic, where an acceptor element is present at crystalgrain boundaries, oxygen is adsorbed at grain boundaries due to theabove-described acceptor element during the secondary firing.Consequently, the dielectric characteristic can be improved.

The present inventor adjusted the composition such that a donor elementwas contained in solid solution in crystal grains and an acceptorelement was present at crystal grain boundaries, and conducted intensiveresearch. As a result, it was found that the characteristics, e.g., theapparent relative dielectric constant ∈r_(APP) and the insulatingproperty, could be improved by improving the crystallinity at a powderstage before sintering, and by making the crystal grains into a finepowder state as much as possible. Furthermore, as a result of intensiveresearch further conducted by the present inventor, it was found that inthe case where the integral width (integrated intensity/peak intensity)β of the (222) face of the crystal face was 0.500° or less and theaverage powder grain size was 1.0 μm or less, a good insulating propertycould be obtained because the apparent relative dielectric constant∈r_(APP) became 5,000 or more, and the specific resistance log ρ (ρ:Ω·cm) became 10 or more even when the average ceramic grain size ofcrystal grains after sintering was 1.0 μm or less.

The present invention has been made on the basis of the above-describedfindings. A semiconductor ceramic powder according to the presentinvention is characterized by being a SrTiO₃-based grain boundaryinsulation type semiconductor ceramic powder, wherein a donor element iscontained in solid solution in crystal grains and, in addition, anacceptor element is present at least in crystal grain boundaries, theintegral width of (222) face of the crystal face is 0.500° or less, andthe average powder grain size of crystal grains is 1.0 μm or less.

Furthermore, the semiconductor ceramic powder according to the presentinvention is characterized in that the above-described donor elementpreferably contains at least one element selected from La, Sm, Dy, Ho,Y, Nd, Ce, Nb, Ta, and W.

Moreover, the semiconductor ceramic powder according to the presentinvention is characterized in that the above-described acceptor elementpreferably contains at least one element selected from Mn, Co, Ni, andCr.

In addition, a semiconductor ceramic according to the present inventionis characterized by being produced through sintering of theabove-described semiconductor ceramic powder.

In this regard, it is desirable to specify the average ceramic grainsize of crystal grains to be 1.0 μm or less in order to obtain thelarge-capacity monolithic semiconductor ceramic capacitor throughreduction in thickness and multilayering. However, crystal grains becomecoarse due to grain growth during the firing treatment. Therefore, evenwhen the average powder grain size of the semiconductor ceramic powderis 1.0 μm or less, sometimes, it is difficult to specify the averageceramic grain size to be 1.0 μm or less merely by adjusting thecomposition.

The present inventor conducted further intensive research and it wasdiscovered that the grain growth of crystal grains during the firingtreatment was suppressed and the average ceramic grain size of crystalgrains was able to be specified to be 1.0 μm or less by conducting thefiring treatment while the firing temperature was set at a temperaturelower than the calcination temperature.

That is, the semiconductor ceramic according to the present invention ischaracterized by being produced through sintering at a temperature lowerthan the calcination temperature during production of theabove-described semiconductor ceramic powder.

Furthermore, a monolithic semiconductor ceramic capacitor according tothe present invention is characterized by including internal electrodesdisposed in a component element assembly and external electrodes, whichcan be electrically connected to the above-described internal electrodesand which are disposed on surfaces of the above-described componentelement assembly, wherein the above-described component element assemblyis formed from the above-described semiconductor ceramic.

ADVANTAGES

According to the semiconductor ceramic powder of the present invention,the donor element, e.g., La or Sm, is contained as a solid solution inthe crystal grains and, in addition, the acceptor element, e.g., Mn orCo, is present at least in the crystal grain boundaries, the integralwidth of (222) face of the crystal face is 0.500° or less, and theaverage powder grain size of crystal grains is 1.0 μm or less.Consequently, the electrical characteristics of the apparent relativedielectric constant ∈r_(APP) of 5,000 or more and the specificresistance log ρ (ρ: Ω·cm) of 10 or more can be obtained even when theaverage ceramic grain size of crystal grains after sintering is 1.0 μmor less.

Furthermore, the semiconductor ceramic according to the presentinvention is produced through sintering of the above-describedsemiconductor ceramic powder. Therefore, as described above, theapparent relative dielectric constant ∈r_(APP) becomes a large 5,000 ormore and the specific resistance log ρ (ρ: Ω·cm) becomes 10 or more, sothat an excellent insulating property is exhibited and a semiconductorceramic having good electrical characteristics can be obtained.

Moreover, the semiconductor ceramic is produced through sintering at atemperature lower than the calcination temperature during production ofthe above-described semiconductor ceramic powder. Therefore, the averageceramic grain size of crystal grains can be reduced to 1.0 μm or less,so that a semiconductor ceramic suitable for reduction in thickness andmultilayering can be obtained.

In addition, the component capacitor element assembly is formed from theabove-described semiconductor ceramic. Therefore, even in the case wherethe thickness of the semiconductor ceramic layer constituting thecomponent element assembly is reduced to about 1.0 μm, it becomespossible to realize a large-capacity high-performance monolithicsemiconductor ceramic capacitor, which has a large apparent relativedielectric constant ∈r_(APP) and a large specific resistance, throughreduction in thickness and multilayering, whereas it has not been ableto realize this with respect to the monolithic ceramic capacitor in therelated art.

In particular, the SrTiO₃-based grain boundary insulation typesemiconductor ceramic has a varistor function. Therefore, asurge-resistant capacitor and surge-absorbing capacitor can be realized,whereas it is believed to be impossible to realize the same with respectto the monolithic ceramic capacitor in the related art.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram for explaining the significance of the integralwidth β of (222) face.

FIG. 2 is a sectional view schematically showing an embodiment of amonolithic semiconductor ceramic capacitor produced by using asemiconductor ceramic according to the present invention.

FIG. 3 is a diagram showing an example of a firing profile and changesin the electromotive force with time.

FIG. 4 is an X-ray diffraction chart of Sample No. 1.

REFERENCE NUMERALS

-   -   1 component element assembly    -   1 a to 1 g semiconductor ceramic layer    -   2 internal electrode    -   3 a, 3 b external electrode

BEST MODES FOR CARRYING OUT THE INVENTION

Next, the embodiments according to the present invention will bedescribed in detail.

A semiconductor ceramic powder as an embodiment of the present inventionis a SrTiO₃-based grain boundary insulation type semiconductor ceramicpowder, wherein a donor element is contained as a solid solution incrystal grains and, in addition, an acceptor element is present at leastin the crystal grain boundaries, the integral width β of (222) face ofthe crystal face is 0.500° or less, and the average powder grain size ofcrystal grains is specified to be 1.0 μm or less.

The ceramic can be converted to a semiconductor by allowing crystalgrains to contain the donor element as a solid solution. Furthermore,regarding the grain boundary insulation type semiconductor ceramiccapacitor, after the composition is converted to a semiconductor,secondary firing is conducted and, thereby, crystal grain boundaries areconverted to insulators. In this case, if the acceptor element ispresent at the crystal grain boundaries, oxygen is adsorbed by the grainboundaries due to the above-described acceptor element during thesecondary firing. Consequently, the dielectric characteristics can beimproved.

In this situation, it is difficult to obtain a semiconductor ceramichaving desired characteristics in which the apparent relative dielectricconstant ∈r_(APP) is 5,000 or more, the specific resistance log ρ (ρ:Ω·cm) is 10 or more, and an insulating property is excellent, merely byadjusting the contents of the donor element and the acceptor element.

Research by the present inventor made it clear that the crystallinity ofcrystal grains at a powder state before sintering had an influence onthe electrical characteristics of the semiconductor ceramic.

The crystallinity of crystal grains at a powder state before sinteringwas evaluated on the basis of the integral width (integratedintensity/peak intensity) β, as shown in FIG. 1. As a result, it wasmade clear that the electrical characteristics were able to be improvedby adjusting the composition component in such a way as to come into ahighly crystalline state in which the integral width β of (222) face ofthe crystal face was 0.500° or less.

It was always clear that even when the above-described integral width βwas 0.500° or less, a sufficient improvement of the electricalcharacteristics was not achieved in the case where the average powdergrain size of crystal grains exceeded 1.0 μm.

Subsequently, the composition component and the calcination temperaturewere adjusted, the semiconductor ceramic powder having theabove-described integral width β of 0.500° or less and the averagepowder grain size of crystal grains of 1.0 μm or less was produced andsintered, and the electrical characteristics were measured. As a result,it was made clear that a semiconductor ceramic having an apparentrelative dielectric constant ∈r_(APP) of 5,000 or more, a specificresistance log ρ (ρ: Ω·cm) of 10 or more, and a good insulating propertywas able to be obtained stably.

When merely the above-described integral width β is 0.500° or less, orin the case where merely the average powder grain size of crystal grainsbefore sintering is 1.0 μm or less, desired electrical characteristicscannot be obtained yet. The semiconductor ceramic having desiredelectrical characteristics, (the apparent relative dielectric constant∈r_(APP) is 5,000 or more, the specific resistance log ρ (ρ: Ω·cm) is 10or more, and an insulating property is good) can be obtained bysatisfying both the above-described integral width β of 0.500° or lessand the average powder grain size of crystal grains before sintering of1.0 μm or less.

For example, in the case where the integral width β exceeds 0.500°, evenwhen the average powder grain size of crystal grains before sinteringcorresponds to that of very fine grains (for example, 0.2 μm or less),the specific resistance log ρ (ρ: Ω·cm) is extremely reduced to theextent that an insulating property in itself does not become apparent.If the above-described integral width β exceeds 0.500°, even when theaverage powder grain size corresponds to that of the above-describedvery fine grains, the grains more than double through grain growthduring firing. Moreover, the reoxidation performance is extremelyreduced and, thereby, the specific resistance is reduced extremely tothe extent that the insulating property in itself does not becomeapparent even when a capacitor is formed.

The molar content of the donor element is not specifically limited.However, 2.0 mol or less relative to 100 mol of Ti element ispreferable. This is because if the donor element exceeds 2.0 molrelative to 100 mol of Ti element, the sinterability deteriorates and areduction in apparent relative dielectric constant ∈r_(APP) may beinvited. In this connection, 1.0 mol or less relative to 100 mol of Tielement is more preferable, and further preferably, 0.8 to 1.0 mol isdesirable.

The donor element is not specifically limited as long as the element iscontained as a solid solution in crystal grains and functions as adonor. For example, rare earth elements, e.g., La, Sm, Dy, Ho, Y, Nd,and Ce, and Nb, Ta, W, and the like can be used.

Likewise, the molar content the acceptor element present in crystalgrain boundaries is not specifically limited, but 0.1 to 1.0 molrelative to 100 mol of Ti element is preferable. This is because if themolar content of the acceptor element exceeds 1.0 mol relative to 100mol of Ti element, reduction in apparent relative dielectric constant∈r_(APP) and insulating property may be invited, while in the case ofless than 0.1 mol, it may be difficult for the dielectriccharacteristics and the insulating property to become apparent. In thisconnection, more preferably, about 0.5 mol relative to 100 mol of Tielement is desirable.

It is indispensable that the acceptor element is present at least in thecrystal grain boundaries. However, the acceptor element may also becontained as a solid solution in the crystal grains within the bounds ofnot affecting the characteristics. In this connection, as for such anacceptor element, transition metal elements, e.g., Mn, Co, Ni, and Cr,can be used.

It is also preferable that a low-melting point oxide within the range of0.1 mol or less relative to 100 mol of Ti element is added to theabove-described semiconductor ceramic powder, in particular at crystalgrain boundaries. The sinterability can be improved and, in addition,segregation of the above-described acceptor element into crystal grainboundaries can be facilitated by adding such a low-melting point oxide.

In this connection, if the molar content of the low-melting point oxideexceeds 0.1 mol relative to 100 mol of Ti element, a reduction inapparent relative dielectric constant ∈r_(APP) may be invited.Therefore, in the case where the low-melting point oxide is added, 0.1mol or less relative to 100 mol of Ti element is preferable, asdescribed above.

The low-melting point oxide is not specifically limited, and SiO₂, glassceramic containing B or alkali metal element (K, Li, Na, or the like),copper-tungsten oxide, and the like can be used. However, SiO₂ is usedpreferably.

In addition, the molar ratio m of the Sr site to the Ti site is notspecifically limited insofar as m is in the vicinity of thestoichiometric composition (m=1.000). It is preferable that0.995≦m≦1.020 is satisfied. This is because, if the blend molar ratio mbecomes less than 0.995, the average powder grain size of crystal grainsmay become larger than 1.0 μm, while if the molar ratio m exceeds 1.020,a deviation from the stoichiometric composition increases and, thereby,sintering may become difficult. In this connection, preferably, themolar ratio m further satisfies 0.995≦m≦1.010, and more preferably1.000<m≦1.010.

The semiconductor ceramic is obtained by sintering the above-describedsemiconductor ceramic powder. At that time, it is preferable that thefiring temperature is set at a temperature lower than the calcinationtemperature during production of the semiconductor ceramic powder.

The average powder grain size of crystal grains can be controlled at 1.0μm or less by adjusting the composition range and selecting thecalcination temperature. However, sometimes, it is difficult to controlthe average ceramic grain size of crystal grains of the semiconductorceramic (sintered body) at 1 μm or less merely by adjusting thecomposition and temperature, and a reduction in thickness and anincrease in capacity may be hindered. This is because even when theaverage powder grain size of the semiconductor ceramic powder aftercalcination is 1.0 μm or less, which is in the state of a fine powder,grain growth of crystal grains occurs when conducting a firing treatmentsuch that the crystal grains become coarse. That is, the case where theaverage powder grain size of the crystal grains of the semiconductorceramic powder is sufficiently small relative to 1.0 μm is particular,and also in the case where the average powder grain size of crystalgrains is close to 1.0 μm, grain growth of crystal grains occurs duringthe firing treatment, so that the crystal grains become coarse.Consequently, sometimes, it becomes difficult to control the averageceramic grain size of crystal grains at 1.0 μm or less.

Therefore, it is preferable that grain growth of crystal grains issuppressed by conducting the firing treatment while the firingtemperature is set at a temperature lower than the calcinationtemperature. Consequently, the average ceramic grain size of crystalgrains can be specified to be 1.0 μm or less reliably.

As described above, a semiconductor ceramic having an apparent relativedielectric constant ∈r_(APP) of 5,000 or more, a specific resistance logρ (ρ: Ω·cm) of 10 or more, and an excellent insulating property can beobtained in spite of the fact that the average ceramic grain size ofcrystal grains is 1.0 μm or less, which corresponds to that of very finegrains.

FIG. 2 is a sectional view schematically showing an embodiment of amonolithic semiconductor ceramic capacitor produced by using asemiconductor ceramic according to the present invention.

In the monolithic semiconductor ceramic capacitor, internal electrodes2(2 a to 2 f) are embedded in a component element assembly 1 formed fromthe semiconductor ceramic of the present invention and, in addition,external electrodes 3 a and 3 b are disposed on both end portions of thecomponent element assembly 1.

That is, the component element assembly 1 is composed of a monolithicsintered body in which a plurality of semiconductor ceramic layers 1 ato 1 g and internal electrodes 2 a to 2 f are laminated alternately. Theinternal electrodes 2 a, 2 c, and 2 e are electrically connected to theexternal electrode 3 a, and the internal electrodes 2 b, 2 d, and 2 fare electrically connected to the external electrode 3 b. Furthermore,capacitances are formed between opposed surfaces of the internalelectrodes 2 a, 2 c, and 2 e and the internal electrodes 2 b, 2 d, and 2f.

Next, a method for manufacturing the above-described semiconductorceramic capacitor will be described.

Initially, each of a Sr compound, e.g., SrCO₃, a donor compoundcontaining a donor element, e.g., La or Sm, an acceptor compound, e.g.,Mn or Co, and a Ti compound, e.g., TiO₂, having a specific surface areaof preferably 10 m²/g or more (average grain size: about 0.1 μm or less)is prepared as a ceramic raw material. Predetermined amounts of theseceramic raw materials are weighed.

Subsequently, the resulting weighed material is blended with apredetermined amount of dispersing agent and is put into a ball milltogether with pulverization media, e.g., PSZ (Partially StabilizedZirconia) balls, and water. Wet-mixing is conducted sufficiently in theball mill to produce a slurry.

Then, the resulting slurry is heated (dried), and thereafter, acalcination treatment is conducted in an air atmosphere at apredetermined temperature (for example, 1,300° C. to 1,450° C.) forabout 2 hours, so as to produce a calcined powder.

Next, predetermined amounts of low-melting point oxides, e.g., SiO₂, areweighed as necessary. Subsequently, these low-melting point oxides areadded to the above-described calcined powder, pure water, and thedispersing agent, as necessary, and wet-mixing is conductedsufficiently, followed by heating (drying). Thereafter, a heat treatmentis conducted in an air atmosphere at a predetermined temperature (forexample, 600° C.) for about 5 hours, so as to produce a heat-treatedpowder.

Then, the resulting heat-treated powder is blended with appropriateamounts of organic solvent, e.g., toluene or alcohol, and a dispersingagent and, thereafter, is put into a ball mill again together with theabove-described pulverization media. Wet-mixing is conductedsufficiently in the ball mill. Subsequently, appropriate amounts oforganic binder and plasticizer are added and wet-mixing is conducted forsufficiently long time so that a ceramic slurry is thereby produced.

Next, the ceramic slurry is subjected to shaping by using a shapingmethod, e.g., a doctor blade method, a lip coater method, or a diecoater method, so as to produce a ceramic green sheet in such a way thatthe thickness after firing becomes a predetermined thickness (forexample, 1 to 2 μm).

Thereafter, screen printing, gravure printing, vacuum evaporation, orsputtering is applied to the ceramic green sheet by using anelectrically conductive paste for an internal electrode, so as to forman electrically conductive film with a predetermined pattern on thesurface of the above-described ceramic green sheet.

In this connection, the electrically conductive material contained inthe electrically conductive paste for an internal electrode is notspecifically limited. However, it is preferable to use a base metalmaterial, e.g., Ni or Cu.

Subsequently, the predetermined number of ceramic green sheets providedwith the electrically conductive film are laminated in a predetermineddirection and, in addition, outside layer ceramic green sheets providedwith no electrically conductive film are laminated. Then, contactbonding is conducted, and cutting into a predetermined dimension isconducted, so as to produce a ceramic laminate.

Thereafter, a debinding treatment is conducted in an air atmosphere at atemperature of 200° C. to 300° C. and, furthermore, in a weak reducingatmosphere at a temperature of 700° C. to 800° C., as necessary.Subsequently, a firing furnace brought into a reducing atmosphere, inwhich a H₂ gas and a N₂ gas constitute a predetermined flow rate ratio(for example, H₂/N₂=0.025/100 to 1/100), is used, and primary firing isconducted in the firing furnace at a temperature of 1,150° C. to 1,300°C. for about 2 hours, so as to convert the ceramic laminate to asemiconductor. That is, the primary firing is conducted at a lowtemperature lower than or equal to the calcination temperature (1,300°C. to 1,450° C.), so as to convert the ceramic laminate to thesemiconductor.

In this primary firing treatment, the oxygen partial pressure in thefiring furnace is increased sharply at the start of cooling after firingso as to set the oxygen partial pressure at the start of cooling (oxygenpartial pressure in cooling) at 1.0×10⁴ times the oxygen partialpressure in the firing process (oxygen partial pressure in firing) ormore, and a cooling treatment is conducted.

That is, in the present embodiment, the oxygen partial pressure in thefiring furnace is increased sharply at the start of cooling after firingby supplying large amounts of steam into the firing furnace and,furthermore, decreasing the flow rate of supply of the H₂ gas into thefiring furnace by a predetermined amount (for example, 1/10).Specifically, the cooling treatment is conducted while the ratio of theoxygen partial pressure in cooling to the oxygen partial pressure infiring, that is, the oxygen partial pressure ratio ΔPO₂, is set at1.0×10⁴ or more. Consequently, a still larger specific resistance can beobtained while the apparent relative dielectric constant ∈r_(APP) of5,000 or more is ensured.

In this connection, the above-described “at the start of cooling”includes not only the time of entrance into the cooling process, butalso the short time in which the temperature in the furnace is loweredfrom the maximum temperature by a predetermined temperature (forexample, 30° C. to 50° C.) after entrance into the cooling process.

The reasons for setting of the oxygen partial pressure in cooling at1.0×10⁴ times the oxygen partial pressure in firing or more will bedescribed with reference to FIG. 3.

FIG. 3 is a diagram showing the firing profile and changes in theelectromotive force E with time. The horizontal axis indicates the time(hr), the left vertical axis indicates the temperature (° C.), the rightvertical axis indicates the electromotive force E (V), a solid lineindicates the firing profile, and alternate long and short dashed linesindicate the changes in the electromotive force with time.

In the firing profile, the temperature in the furnace is raised asindicated by an arrow A (temperature raising process) at the start ofthe firing treatment. Subsequently, the maximum firing temperature Tmax(in the present embodiment, 1,150° C. to 1,300° C.) is kept for about 2hours as indicated by an arrow B (firing process). Thereafter, thetemperature in the furnace is lowered as indicated by an arrow C so asto cool the fired material (cooling process).

The Nernst equation represented by Mathematical expression (1) holdsbetween the electromotive force E (V) and the oxygen partial pressurePO₂ (atm) in the firing furnace.E=(2.15×10⁻⁵ ×T)×Ln(PO₂/0.206)  (1)where, T represents an absolute temperature (K) in the firing furnace.

Therefore, the oxygen partial pressure PO₂ can be determined bymeasuring the electromotive force E.

Then, steam was supplied into the firing furnace at the time of entranceinto the cooling process and, furthermore, the flow rate of supply ofthe hydrogen gas into the firing furnace was decreased, as necessary,while changes in electromotive force E with time in the firing furnacewas measured with a direct insertion type zirconia oxygen sensor. As aresult, it was made clear that, as indicated by the alternate long andshort dashed lines in FIG. 3, the electromotive force E always becomes alocal minimum at the point in time when the temperature in the furnacewas lowered from the maximum firing temperature Tmax by a predeterminedtemperature ΔT (for example, 30° C. to 50° C.) and, thereafter, theelectromotive force E increased gradually. Therefore, according tomathematical expression (1), the oxygen partial pressure PO₂ becomes alocal maximum at the point in time when the temperature in the furnaceis lowered from the maximum firing temperature Tmax by the predeterminedtemperature ΔT.

The present inventor repeatedly conducted experiments wherein the localmaximum oxygen partial pressure PO₂ was assumed to be the oxygen partialpressure in cooling, the oxygen partial pressure at the maximum firingtemperature Tmax was assumed to be the oxygen partial pressure infiring, and the oxygen partial pressure ratio ΔPO₂ (=oxygen partialpressure in cooling/oxygen partial pressure in firing) of the two waschanged variously while the flow rate of supply of the steam and theflow rate of supply of the H₂ gas into the furnace were adjusted. As aresult, it was made clear that a still larger specific resistance wasable to be obtained while the apparent relative dielectric constant∈r_(APP) of 5,000 or more was ensured by specifying the above-describedoxygen partial pressure ratio ΔPO₂ to be 1.0×10⁴ or more.

Consequently, in the present embodiment, primary firing is conductedwhile the oxygen partial pressure ratio ΔPO₂ is set at 1.0×10⁴ or moreand then the cooling treatment is conducted.

After the ceramic laminate is converted to a semiconductor through theprimary firing as described above, secondary firing is conducted in aweak reducing atmosphere, in an air atmosphere, or in an oxidizingatmosphere for 1 hour at a low temperature of 600° C. to 900° C. inorder that the internal electrode material, e.g., Ni or Cu, is notoxidized, so as to reoxidize the semiconductor ceramic and, thereby,form a grain boundary insulating layer. In this manner, the componentelement assembly 1 is produced, in which the internal electrodes 2 areembedded.

Subsequently, an electrically conductive paste for an external electrodeis applied to both end surfaces of the component element assembly 1, abaking treatment is conducted and, thereby, the external electrodes 3 aand 3 b are formed. In this manner, the monolithic semiconductor ceramiccapacitor is produced.

In this connection, an electrically conductive material contained in theelectrically conductive paste for an external electrode is notspecifically limited. However, it is preferable to use materials such asGa, In, Ni, and Cu, and it is also possible to form an Ag electrode onan electrode.

Alternatively, as for the method for forming the external electrodes 3 aand 3 b, the electrically conductive paste for an external electrode maybe applied to both end surfaces of the ceramic laminate and, thereafter,a firing treatment may be conducted at the same time with the ceramiclaminate.

In the present embodiment, the monolithic semiconductor ceramiccapacitor is produced by using the above-described semiconductorceramic. Therefore, the layer thickness of each of the semiconductorceramic layers 1 a to 1 g can be reduced to 1.0 μm or less. Even in thecase where the layer thickness is reduced as described above, it becomespossible to realize a large-capacity high-performance monolithicsemiconductor ceramic capacitor, which has a large apparent relativedielectric constant ∈r_(APP) of 5,000 or more per layer and a largespecific resistance log ρ (ρ: Ω·cm) of 10 or more, through reduction inthickness and multilayering, whereas it has not been able to realize thesame with respect to the monolithic ceramic capacitor in the relatedart. Furthermore, it is not necessary to take the polarity intoconsideration, good handleability is exhibited, and the resistance islow even in high frequencies as compared with large-capacity tantalumcapacitors. Therefore, there is usefulness as alternatives to thesetantalum capacitors.

As is described above, it is known that a SrTiO₃-based grain boundaryinsulation type semiconductor ceramic has varistor characteristic. Inthe present embodiment, since the average ceramic grain size of crystalgrains is 1.0 μm or less, which corresponds to that of fine grains, thevaristor voltage can increase. Therefore, uses for a general purposecapacitor are expanded by the use as a capacitor in a usual fieldstrength region (for example, 1 V/μm), in which the voltage-currentcharacteristic exhibits linearity. In addition, since the varistorcharacteristic is provided, breakage of the element can be preventedeven when an abnormally high voltage is applied to the element, so thata capacitor exhibiting excellent reliability can be obtained.

Furthermore, since the varistor voltage can increase, as describedabove, a capacitor, which can avoid breakage against a surge voltage andthe like, can be realized. That is, a low-capacity capacitor used for anESD (electro-static discharge) application is required to have asurge-resistant characteristic. In the case where a breakage voltage ishigh, it is possible to use the capacitor for an application as anESD-resistant guarantee capacitor, e.g., a surge-resistant and asurge-absorbing capacitor.

The present invention is not limited to the above-described embodiment.FIG. 2 shows the monolithic semiconductor ceramic capacitor, in which aplurality of semiconductor ceramic layers 1 a to 1 g and the internalelectrodes 2 a to 2 f are laminated alternately. However, a monolithicsemiconductor ceramic capacitor can have a structure in which aninternal electrode is formed through evaporation or the like on asurface of a single sheet (for example, the thickness is about 200 μm)of a semiconductor ceramic and several layers of the single sheets (forexample, 2 or 3 layers) are bonded together with an adhesive. Such astructure is effective for a monolithic semiconductor ceramic capacitorused for low capacity application, for example.

In the above-described embodiment, the solid solution is produced by asolid phase method. However, the method for producing the solid solutionis not specifically limited and any method, for example, a hydrothermalsynthesis method, a sol•gel method, a hydrolysis method, or acoprecipitation method, can be used.

Furthermore, in the above-described embodiment, the secondary firing(reoxidation treatment) to form the grain boundary insulating layer canbe conducted in an air atmosphere. However, the desired operation andeffect can be obtained even when the oxygen concentration is reduced, asnecessary, to some extent as compared with that of an air atmosphere.

Moreover, the above-described monolithic semiconductor ceramic capacitoris produced by conducting a cooling treatment in the primary firingtreatment while the oxygen partial pressure at the start of cooling isset at 1.0×10⁴ times the oxygen partial pressure in the firing process.However, even in the case where the primary firing treatment isconducted without specifically changing the oxygen partial pressure inthe firing furnace, it is possible to obtain an apparent relativedielectric constant ∈r_(APP) of 5,000 or more and a log ρ (ρ: Ω·cm) of10 or more. In this case, the semiconductor ceramic can be producedroughly as described below.

That is, predetermined amounts of donor compound and acceptor compoundare weighed, and a predetermined amount of predetermined ceramic rawmaterial is further weighed. After mixing and pulverization areconducted, a calcination treatment is conducted so as to produce acalcined powder. Furthermore, a low-melting point oxide, e.g., SiO₂, isweighed, as necessary, and this is mixed with the above-describedcalcined powder. A heat treatment is conducted so as to produce aheat-treated powder, and the heat-treated powder is subjected to aprimary firing treatment in a reducing atmosphere. Thereafter, asecondary firing treatment is conducted in a weak reducing atmosphere,in an air atmosphere, or in an oxidizing atmosphere and, thereby, asemiconductor ceramic can be produced.

Next, examples of the present invention will be described specifically.

EXAMPLES

As for ceramic raw materials, SrCO₃, LaCl₃, MnCl₂, and TiO₂ having aspecific surface area of 30 m²/g (average grain size: about 30 nm) wereprepared. These ceramic raw materials were weighed in such a way thatthe crystal grain composition of the ceramic had the molar contentsshown in Table 1 relative to 100 mol of the Ti element. Furthermore, 2parts by weight of polycarboxylic acid ammonium salt relative to 100parts by weight of the weighed material was added as a dispersing agent.Subsequently, the mixture was put into a ball mill together with PSZballs having a diameter of 2 mm and water. Wet-mixing was conducted for16 hours in the ball mill so as to produce a slurry.

Then, the resulting slurry was heated to vaporize volatile materials anddried. Thereafter, a calcination treatment was conducted in an airatmosphere at a calcination temperature shown in Table 1 for 2 hours, soas to obtain a calcined powder.

Next, a MnCl₂ aqueous solution and a SiO₂ sol solution were added to theabove-described calcined powder in such a way that the molar contents ofMn element and SiO₂ in crystal grains became as shown in Table 1relative to 100 mol of the Ti element. Pure water and a dispersingagent, as necessary, were further added and wet-mixing was conducted for16 hours, followed by vaporization of volatiles and drying. Thereafter,a heat treatment was conducted in an air atmosphere at a temperature of600° C. for 5 hours, so as to produce a heat-treated powder. In thisconnection, a MnO₂ sol may be used instead of the MnCl₂ aqueoussolution, and tetraethoxysilane (Si(OC₂H₅)₄) may be used instead of theSiO₂ sol solution.

Then, the above-described heat-treated powder was blended withappropriate amounts of organic solvent, e.g., toluene or alcohol, anddispersing agent and, was put into a ball mill again together with thePSZ balls having a diameter of 2 mm. Wet-mixing was conducted for 4hours in the ball mill. Subsequently, appropriate amounts of polyvinylbutyral (PVB) serving as a binder and dioctyl phthalate (DOP) serving asa plasticizer were added and a wet-mixing treatment was furtherconducted for 16 hours, so that a ceramic slurry was thereby produced.

Next, the ceramic slurry was subjected to shaping by using the lipcoater method, so as to produce a ceramic green sheet having a thicknessof about 3.2 μm. Thereafter, the resulting ceramic green sheets werestamped into a predetermined size, and were stacked in such a way thatthe thickness became about 0.5 mm. Thermocompression bonding wasconducted, so as to produce a ceramic compact.

Subsequently, the resulting ceramic compact was cut into 5 mm in length,5 mm in width, and 0.5 mm in thickness. Then, a debinding treatment wasconducted in an air atmosphere at a temperature of 250° C. for 6 hoursand, furthermore, in a weak reducing atmosphere of 1.4×10⁻¹⁵ MPa at atemperature of 800° C. for 5 hours.

Thereafter, primary firing was conducted in a strong reducingatmosphere, in which the flow rate ratio (H₂/N₂) of a H₂ gas to a N₂ gaswas specified to be 1/100, at a temperature of 1,150° C. to 1,250° C.for 2 hours, so as to effect conversion to a semiconductor. In addition,at this time, a cooling treatment was conducted until the temperature ofthe firing furnace became 800° C. while the oxygen partial pressure PO₂was adjusted in such a way that the oxygen partial pressure ratio ΔPO₂(=oxygen partial pressure in cooling/oxygen partial pressure in firing)became 1.0×10⁴. That is, the cooling treatment was conducted while azirconia oxygen sensor was inserted into the firing furnace and theelectromotive force E, i.e. the oxygen partial pressure PO₂, wasmeasured, steam was supplied into the firing furnace at the time ofstart of the cooling process and, in addition, the flow rate of supplyof the H₂ gas was decreased in such a way that the flow rate ratio(H₂/N₂) of the H₂ gas to the N₂ gas was changed from 1/100 to 0.1/100,so as to control the oxygen partial pressure ratio ΔPO₂ at 1.0×10⁴described above.

Then, a secondary firing was conducted in an air atmosphere at atemperature of 800° C. for 1 hour as a reoxidation treatment, so that agrain boundary insulation type semiconductor ceramic was produced.

Subsequently, In—Ga was applied to both end surfaces, so as to form theexternal electrodes. In this manner, samples of Sample Nos. 1 to 14 wereproduced.

Next, for each of these samples of Sample Nos. 1 to 14, the averagepowder grain size, the integral width β of (222) face, the averageceramic grain size, the apparent relative dielectric constant ∈r_(APP),and the specific resistance log ρ (ρ: Ω·cm) were determined.

The average powder grain size was determined by pulverizing theabove-described sample after the above-described debinding treatmentinto the shape of a powder, conducting observation with a scanningelectron microscope (SEM), and conducting image analysis of SEMphotographs of a sample surface and a rupture surface.

Furthermore, the integral width β of (222) face was determined from anX-ray diffraction chart on the basis of analysis of the crystalstructure with a parallel optical system by using an X-raydiffractometer (Rint2500: produced by RIGAKU Corporation) under thecondition of a tube voltage of 50 kV and a tube current of 250 mA.

The apparent relative dielectric constant ∈r_(APP) was calculated fromthe measured capacitance and the sample dimension, wherein thecapacitance was measured by using an impedance analyzer (HP4194A:produced by Agilent Technologies) under the condition of a frequency of1 kHz and a voltage of 1 V.

The average ceramic grain size of crystal grains after sintering wasdetermined by conducting observation with a scanning electron microscope(SEM), and conducting image analysis of SEM photographs of a samplesurface and a rupture surface.

The specific resistance log ρ was determined by applying 5 to 500 V ofdirect current voltage for 2 minutes, measuring the insulationresistance IR at a field strength of 1 V/μm on the basis of the leakagecurrent thereof, and calculating the specific resistance ρ from theinsulation resistance IR and the sample dimension, followed byconversion to common logarithm.

Table 1 shows compositions of crystal grains and grain boundaries,calcination temperatures, and measurement results of Sample Nos. 1 to14. In this connection, in Table 1, the number of moles of each of La,Mn, and SiO₂ represents the molar content relative to 100 mol of Ti.

TABLE 1 Crystal grain Crystal grain boundary Molar Molar SemiconductorSemiconductor ceramic content content ceramic powder (sintered body)relative to relative to Average Integral Average Apparent 100 mol of 100mol of powder width β ceramic relative Specific Ti element Ti elementCalcination grain of (222) grain dielectric resistance Sample Molarratio La Mn Mn SiO₂ temperature size face size constant logρ No. m (—)(mol) (mol) (mol) (mol) (° C.) (μm) (°) (μm) εr_(APP) (ρ: Ω · cm) 11.010 0.8 0.0080 0.5 0.1 1400 0.51 0.400 0.54 5310 11.4 2 1.010 0.80.0080 0.5 0.1 1350 0.49 0.500 0.52 5010 11.3 3 1.005 0.8 0.0400 0.5 0.11375 0.53 0.410 0.57 5470 11.2 4 1.005 0.8 0.0800 0.5 0.1 1375 0.610.395 0.68 5910 11.1 5 1.000 0.8 0.0400 0.5 0.1 1375 0.65 0.390 0.715280 10.9 6 1.000 0.8 0.0800 0.5 0.1 1375 0.68 0.385 0.73 5360 10.8 71.010 0.85 0 0.5 0.1 1400 0.58 0.405 0.65 5910 10.3 8 1.005 0.8 0 0.50.1 1375 0.53 0.415 0.64 5080 10.2 9 1.000 0.4 0 0.5 0.1 1400 0.55 0.3880.58 5560 10.8 10  1.000 1.2 0 0.5 0.1 1400 0.50 0.420 0.53 5030 11.011* 0.990 0.8 0.0080 0.5 0.1 1400 1.50 0.450 1.60 4500 9.8 12* 1.010 0.80.0800 0.5 0.1 1300 0.45 0.520 0.51 2830 11.2 13* 1.000 0.8 0 0.5 0.11200 0.18 0.525 0.37 2740 <6 14* 1.000 0.8 0 0.5 0.1 1100 0.12 0.5350.31 2650 <6 *asterisked sample numbers indicate samples which are outof the present invention

In Sample No. 11, the average powder grain size of the semiconductorceramic powder was 1.50 μm, which exceeded 1.0 μm. Therefore, theaverage ceramic grain size of the sintered body was 1.60 μm and wascoarse. As a result, the apparent relative dielectric constant ∈r_(APP)was 4,500, which was less than 5,000, and the specific resistance log ρwas 9.8, which was 10 or less, so that the insulating propertydeteriorated.

In Sample No. 12, the integral width β of (222) face was 0.520°, whichexceeded 0.500. Consequently, it was made clear that the specificresistance log ρ was a good 11.2, but the apparent relative dielectricconstant ∈r_(APP) was significantly reduced to 2,830.

In Sample No. 13, the average powder grain size was 0.18 μm, whichcorresponded to that of very fine grains, but the integral width β of(222) face was 0.525°, which exceeded 0.500. As a result, it was madeclear that the specific resistance log ρ was reduced to less than 6.0and the apparent relative dielectric constant ∈r_(APP) was significantlyreduced to 2,740. The reason for this is believed to be that althoughthe average powder grain size was 0.20 μm or less, which corresponded tothat of very fine grains, the integral width β of (222) face exceeded0.500 and, therefore, the ceramic grain size more than doubled throughgrain growth during firing, and furthermore, the reoxidation performancedeteriorated significantly, and as a result, an insulating property asthe capacitor did not become apparent.

For the same reasons, it was made clear that the average powder grainsize of Sample No. 14 was 0.12 μm, which corresponded to that of veryfine grains, but the integral width β of (222) face was 0.535°, whichexceeded 0.500, and thereby, the specific resistance log ρ was reducedto less than 6.0 and the apparent relative dielectric constant ∈r_(APP)was significantly reduced to 2,650.

On the other hand, in Sample Nos. 1 to 10, the average powder grainsizes of the semiconductor ceramic powders were 0.49 to 0.68 μm and theintegral widths β of (222) face were 0.400° to 0.500°, all of which werewithin the scope of the present invention. Therefore, the averageceramic grain sizes of crystal grains were 0.52 to 0.73 μm, the apparentrelative dielectric constants ∈r_(APP) were 5,010 to 5,910, and thespecific resistances log ρ were 10.2 to 11.4. That is, it was made clearthat a monolithic semiconductor ceramic capacitor having good dielectriccharacteristics and an excellent insulating property was able to beobtained, wherein the apparent relative dielectric constant ∈r_(APP) was5,000 or more and the specific resistance log ρ was 10 or more, althoughthe average ceramic grain size of crystal grains was 1.0 or less.

FIG. 4 is an X-ray diffraction chart of Sample No. 1. The horizontalaxis indicates the diffraction angle 2θ(°) and the vertical axisindicates the X-ray intensity (a.u.).

The integral width β of (222) face shown in FIG. 4 is the result of thecrystallinity evaluation.

1. A semiconductor ceramic powder which is a SrTiO₃-based grain boundaryinsulation type semiconductor ceramic powder containing a donor elementas a solid solution in crystal grains and an acceptor element at leastin crystal grain boundaries, wherein the integral width of (222) face ofthe crystal face is 0.500° or less, and the average powder grain size ofcrystal grains is 1.0 μm or less.
 2. The semiconductor ceramic powderaccording to claim 1, characterized in that the donor element comprisesat least one element selected from the group consisting of La, Sm, Dy,Ho, Y, Nd, Ce, Nb, Ta, and W.
 3. The semiconductor ceramic powderaccording to claim 2, characterized in that the acceptor elementcomprises at least one type of element selected from the groupconsisting of Mn, Co, Ni, and Cr.
 4. A semiconductor ceramic which is asintered semiconductor ceramic powder according to claim
 2. 5. Thesemiconductor ceramic according to claim 4, characterized by having beensintering at a temperature lower than the calcination temperature of thesemiconductor ceramic powder.
 6. A monolithic semiconductor ceramiccapacitor comprising internal electrodes disposed in a component elementassembly and having external electrodes electrically connected to theinternal electrodes and which are disposed on surfaces of the componentelement assembly, wherein the component element assembly comprises asemiconductor ceramic according to claim
 4. 7. The semiconductor ceramicpowder according to claim 3, characterized in that the donor element ispresent in an amount of 2 mol or less relative to 100 mols of Ti siteelements and the amount of acceptor element is present in an amount of0.1 to 1 mol relative to 100 mols of Ti site elements.
 8. Thesemiconductor ceramic powder according to claim 7, characterized in thatthe donor element is present in an amount of 1 mol or less relative to100 mols of Ti site elements, and the ratio of Sr site elements to Tisite elements is 0.995 to 1.01.
 9. The semiconductor ceramic powderaccording to claim 8, characterized in that the donor element is presentin an amount of 0.8 to 1 mol or less relative to 100 mols of Ti siteelements, the amount of acceptor element is present in an amount of 0.5mol relative to 100 mols of Ti site elements, and the ratio of Sr siteelements to Ti site elements is 1.00 to 1.01.
 10. A semiconductorceramic which is a sintered semiconductor ceramic powder according toclaim
 9. 11. The semiconductor ceramic according to claim 10,characterized by having been sintering at a temperature lower than thecalcination temperature of the semiconductor ceramic powder.
 12. Amonolithic semiconductor ceramic capacitor comprising internalelectrodes disposed in a component element assembly and having externalelectrodes electrically connected to the internal electrodes and whichare disposed on surfaces of the component element assembly, wherein thecomponent element assembly comprises a semiconductor ceramic accordingto claim
 10. 13. The semiconductor ceramic powder according to claim 1,characterized in that the acceptor element comprises at least one typeof element selected from the group consisting of Mn, Co, Ni, and Cr. 14.A semiconductor ceramic which is a sintered semiconductor ceramic powderaccording to claim
 13. 15. The semiconductor ceramic according to claim14, characterized by having been sintering at a temperature lower thanthe calcination temperature of the semiconductor ceramic powder.
 16. Amonolithic semiconductor ceramic capacitor comprising internalelectrodes disposed in a component element assembly and having externalelectrodes electrically connected to the internal electrodes and whichare disposed on surfaces of the component element assembly, wherein thecomponent element assembly comprises a semiconductor ceramic accordingto claim
 15. 17. A semiconductor ceramic which is a sinteredsemiconductor ceramic powder according to claim
 1. 18. The semiconductorceramic according to claim 17, characterized by having been sintering ata temperature lower than the calcination temperature of thesemiconductor ceramic powder.
 19. A monolithic semiconductor ceramiccapacitor comprising internal electrodes disposed in a component elementassembly and having external electrodes electrically connected to theinternal electrodes and which are disposed on surfaces of the componentelement assembly, wherein the component element assembly comprises asemiconductor ceramic according to claim
 18. 20. A monolithicsemiconductor ceramic capacitor comprising internal electrodes disposedin a component element assembly and having external electrodeselectrically connected to the internal electrodes and which are disposedon surfaces of the component element assembly, wherein the componentelement assembly comprises a semiconductor ceramic according to claim17.